Glass fibre-reinforced polymer structures

A typical layered structure consists of two thin, glass-fibre-reinforced polymer skins bonded to a thick, lightweight honeycomb core (Fig. 4.5a). Such sandwich panels are used in railway carriages and aircraft there are similar structures inside many skins. Other examples are less obvious the space between the outer container and the toughened polystyrene liner of a refrigerator is filled with rigid polyurethane foam. 

Firth I and Cooper D (2001), The Halgavor Bridge - the use of glass-fibre reinforced polymer composites as the primary structural material in new bridge construction , NGCC First Annual Conference andAGM Composites in Construction Through Life Performance, Watford, UK, 30-31 October, 1-11. 

Subclass B2 is formed by the so-called structural composites, in which an outspoken mechanical reinforcement is given to the polymer. Subgroup B21 consists of blends of polymers with compatible anti-plasticizers subgroups B22 are the most important the fibre-reinforced polymer systems. The two components, the polymer matrix and the reinforcing fibbers or filaments (glass, ceramic, steel, textile, etc.) perform different functions the fibrous material carries the load, while the matrix distributes the load the fibbers act as crack stoppers, the matrix as impact-energy absorber and reinforcement connector. Interfacial bonding is the crucial problem. 

Chen, F. and Jones, F. R., Injection moulding of glass fibre reinforced phenolic composites 1. Study of the critical fibre length and the interfacial shear strengtli, Plast., Rubber Composites Proc. Appl, 23, 241 (1995). Termonia, Y., Structure-property relationships in short-fiber-reinforced composites, J. Polym. Set, Polym. Phys. Ed., 32, 969 (1994). 

Fibre reinforced polymers (FRPs) are composed of a reinforcement material (glass, aramid or carbon fibres) surrounded and retained by a (thermoplastic or thermosetting) polymer matrix (unsaturated polyester, epoxy, vinyl ester, or polyurethane). FRPs were first used in the rehahiUtation of reinforced or pre-stressed concrete, but they have also been widely used in the reinforcement of timber structures. 

Noble Polymers supplies a 6% nanoclay-PP composite for the structural seat back of the Honda Accura TL 2004 car. It replaces a 30% glass PP compound in the seat back. Noble Polymers is also targeting the replacement of 20% glass fibre reinforced PP in office furniture parts. Southern Clay Products supplies Cloisite nanocomposite external parts to General Motors for its Impala vehicle, in competition with talc-filled PP. 

Evans AG (1972) A method for evaluating the time-dependent failure characteristics of brittle materials - and its application to polycrystalline alumina. J Mater Sci 7 1137-1146 French MA, Pritchard G (1991) Strength retention of glass/carbon hybrid laminates in aqueous media. In Cardon AH, Verchery G (eds) Durability of polymer based composite systems for structural applications. Elsevier Applied Science, New York, pp 345-354 Friedrich K (1981) Stress corrosion crack propagation in glass fibre reinforced/thermoplastic PET. J Mater Sci 16(12) 3292-3302... 

Polymers below the glass transition temperature are usually rather brittle unless modified by fibre reinforcement or by addition of rubbery additives. In some polymers where there is a small degree of crystallisation it appears that the crystallines act as knots and toughen up the mass of material, as in the case of the polycarbonates. Where, however, there are large spherulite structures this effect is more or less offset by high strains set up at the spherulite boundaries and as in the case of P4MP1 the product is rather brittle. 

Glass reinforced plastics normally have good corrosion resistance against a variety of chemicals and aggessive environments. This is mainly associated with the inertness of the resin, which can be formulated to confer chemical resistance. The main effects of exposure to fluids or vapour is swelling and debonding as a result of absorption by the matrix. Under stress the resistance of resins and fibres to an environment may be reduced through the interaction of the stress with the internal forces. Indeed stress can accelerate the permeation of fluids into the polymer structure in a similar way to temperature. 

The chapter demonstrates that in spite of the incompatibility between hydrophilic natural fibres and hydrophobic polymeric matrices, the properties of natural fibre composites can be enhanced through chemical modifications. The chemical treatments have therefore played a key role in the increased applications of natural fibre composites in the automotive sector. Recent work has also shown that if some of the drawbacks of natural fibres can be adequately addressed, these materials can easily replace glass fibres in many applications. The chapter has also shown that there have been attempts to use natural fibre composites in structural applications, an area which has been hitherto the reserve of synthetic fibres like glass and aramid. The use of polymer nanocomposites in applications of natural fibre-reinforced composites, though at infancy, may provide means to address these efficiencies. Evidence-based life-cycle assessment of natural fibre-reinforced composites is required to build confidence in the green composites applications in automotive sector. 

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